For alternative meanings, see Placebo (disambiguation)

A placebo, from the Latin for "I will please", is a medical treatment (operation, therapy, chemical solution, pill, etc.), which is administered as if it were a therapy, but which has no therapeutic value other than the placebo effect.

Experimenters typically use placebos in the context of a clinical trial, in which a "test" group of patients receive the therapy being tested, and a "control" group receives the placebo. It can then be determined if results from the "test" group exceed those due to the placebo effect. If they do, the therapy or pill given to the "test" group is assumed to have had an effect.

Originally, the placebo was a substance that a well-meaning doctor would give to a patient, telling him that it was a powerful drug (i.e., a pain killer), when in fact it was nothing more than a sugar pill. The subsequent reduction of the patients symptoms was attributed to the patients belief in the drug. This is not how placebos are used today, as the rules that govern clinical trials now insist on full disclosure to subjects who take part. Today, a subject is told that they may receive the drug being tested or they will receive the placebo. This is not the same mental environment that produces the real placebo effect, (or even a nocebo effect, see below). The proper term for the substances used on control group subjects should be "benigncebo" meaning, no intended effect.

Often during these clinical trials, placebos have a positive or negative clinical effect on subjects tested. Most of these effects are presumed to be psychological in nature but placebo effects can at times be predictable and measurable.

A treatment like a placebo but which has a harmful result is called a nocebo (Latin for "I will harm").

See also

• Placebo effect
• Scientific method